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  Continuous clocking of tdi sensorsUSPTO Application #: 20060103725Title: Continuous clocking of tdi sensors Abstract: A method and apparatus for propagating charge through a time division and integration (TDI) sensor is provided. The method and apparatus may be used with the TDI sensor to inspect specimens, the TDI sensor operating to advance an accumulated charge between gates of the TDI sensor. The design comprises controlling voltage waveform shapes for waveforms advancing the accumulated charge between gates in a substantially nonsquare waveform, such as a composite, sinusoidal, or other shaped waveform. Controlling voltage waveform shapes operates at different voltage phases in adjacent gates to provide a substantially de minimis net voltage. (end of abstract)
Agent: Smyrski Law Group, A Professional Corporation - Santa Monica, CA, US Inventors: David Lee Brown, Yung-Ho Chuang USPTO Applicaton #: 20060103725 - Class: 348092000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060103725. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates generally to the field of electronic imaging, and more particularly to inspection of specimens such as semiconductor wafers and photomasks using TDI (Time Delay Integration) sensors. [0003] 2. Description of the Related Art [0004] Many optical systems have the ability to inspect or image features on the surface of a specimen, such as inspecting defects on a semiconductor wafer or photomask. Certain advanced semiconductor defect inspection systems can detect defects on the order of 30 nm in size during a full inspection of a 300 mm diameter wafer. Such defects are seven orders of magnitude smaller than the wafer itself. [0005] These types of optical systems may employ sophisticated sensors, including but not limited to TDI sensors. TDI sensors exhibit increased throughput for wafer inspection systems and photomask inspection systems over other types of sensors by more than one order of magnitude. FIG. 1 illustrates a typical TDI sensor. From FIG. 1, an array of pixels make up the imaging region 101. A current state-of-the-art TDI sensor according to FIG. 1 may contain a 256.times.2048 array or larger image area. In a typical arrangement, a lamp, laser beam, or other bright illumination source illuminates the semiconductor wafer surface. The wafer surface reflects light onto the TDI sensor, and at the points where light strikes the sensor the sensor may generate photoelectrons. [0006] The TDI sensor typically scans a magnified image of the wafer. The sensor continuously accumulates charge as it scans the wafer, and the sensor transfers charge along a column of pixels 102 at generally the same rate at which the sensor moves with respect to the wafer image. In the orientation of FIG. 1, the sensor moves charge vertically from one pixel to the next. [0007] TDI sensors typically contain channel stops 103, represented by the solid vertical lines in FIG. 1. These channel stops 103 prevent the movement of electrons or charge from one column to another within the imaging region 101. Electron movement is generally inhibited until the electrons reach the serial registers 104 at the edge of the sensor, where the serial registers are represented by gray rows of pixels. [0008] When charge reaches the last pixel in a column, the charge moves to the serial register 104. The serial register 104 transfers the charge horizontally, pixel by pixel, until the charge reaches read-out stage and read-out amplifier or amplifiers 105. A transfer gate 106 or similar structure typically controls charge movement between the imaging region 101 and the serial register 104. [0009] Certain TDI sensors have only one read-out amplifier 105, typically positioned at the end of the serial register 104. Other TDI sensors, such as the one shown in FIG. 1, have multiple read-out amplifiers 105 to decrease the time required to read the contents of the pixels in the serial register. [0010] For several reasons, previous TDI sensors exhibit less than optimal functionality. Prior TDI sensors employ a method called "burst clocking," whereby the TDI sensor may transfer a charge from pixel to pixel, where the graph of voltage changes sharply from positive to negative and back again. Previous TDI sensors employing burst clocking do not exhibit optimal speed in transferring the pixel charge, and tend to be highly sensitive to timing jitter. Such sensors can exhibit high levels of power dissipation and have a relatively low charge transfer efficiency. Further, previous TDI sensors tend to exhibit high dispersion of clock waveforms, low modulation transfer functions, and a higher probability of electromigration. Further, TDI sensors employing burst clocking generally do not perform well when environmental conditions or subtle operating changes occur. [0011] It would therefore be beneficial to provide a TDI sensor for use in conjunction with semiconductor wafer or photomask inspections that overcome the foregoing drawbacks present in previously known electronic imaging systems. Further, it would be beneficial to provide a sensing arrangement and overall optical inspection system design having improved functionality over devices exhibiting the negative aspects described herein. SUMMARY OF THE INVENTION [0012] According to one aspect of the present design, there is provided a method and apparatus for propagating charge through a time delay and integration (TDI) sensor. The method and apparatus may be used with the TDI sensor to inspect specimens, the TDI-sensor operating to advance an accumulated charge between gates of the TDI sensor. The design comprises controlling voltage waveform shapes for waveforms advancing the accumulated charge between gates in a substantially nonsquare waveform, such as a composite, sinusoidal, or other shaped waveform. Controlling voltage waveform shapes operate at different voltage phases in adjacent gates to provide a substantially de minimis net voltage fluctuation on ground and DC voltage reference planes. [0013] These and other advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings. DESCRIPTION OF THE DRAWINGS [0014] The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which: [0015] FIG. 1 illustrates construction of a typical high-speed multi-channel TDI sensor; [0016] FIG. 2 shows three neighboring pixels in a column, each pixel comprising three polysilicon gates, with the pixels in seven different states; [0017] FIG. 3 represents graphs of voltage versus time for three gates, namely the a gates, b gates, and c gates, using square wave voltage applications, and a resulting voltage waveform that may appear on an imperfect ground return path; [0018] FIG. 4 illustrates two cross sections of a TDI sensor including three pixels, gates, an insulating layer beneath the gates, and a region of silicon or other suitable semiconductor material; [0019] FIG. 5 represents the sinusoidal voltages applied to the a gates, b gates, and c gates and the resultant de minimis voltage sum; [0020] FIG. 6 shows sinusoidal voltage waveforms for a TDI sensor with two gates per pixel; [0021] FIG. 7 represents sinusoidal voltage waveforms for a TDI sensor having four gates per pixel; Continue reading... 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